Ultrasound and acoustophoresis for water purification

ABSTRACT

Provided herein are systems and methods for separation of particulate from water using ultrasonically generated acoustic standing waves.

RELATED APPLICATIONS

This application claims priority from U.S. Provisional PatentApplication No. 61/261,686 filed on Nov. 16, 2009 and U.S. ProvisionalPatent Application No. 61/261,676 filed on Nov. 16, 2009, both of whichare incorporated, herein, by reference in their entireties.

TECHNICAL FIELD

The subject matter described herein relates to the use of ultrasonicallygenerated acoustic standing waves to achieve trapping, concentration,and separation of suspended-phase components and thereby remove suchcontaminants from a fluid medium such as water.

BACKGROUND

There is great interest and need for water purification for developingcountries. The world population is approximately 6.7 billion people andis expected to be over 8 billion by 2050. Roughly 1.1 billion people inthe world lack access to safe drinking water. Available water sourcescan be contaminated by pathogens. Roughly 2.2 million die each year fromconsumption of pathogen contaminated water and 9500 children die eachday.

Most of the work reported in the literature for pathogen removal fromwater involves replaceable filter units. These units generally consistof packed cartridges, filter membranes, or special filter papers. Thoughorganisms over 10 micron can be easily captured by these techniques,smaller organisms including bacterial spores in the size range of 1micron are typically not captured with sufficient efficiency.

SUMMARY

The current subject matter provides, among other possible advantages, asolid-state, low-cost alternative to filter cartridges and filtermembranes that is capable of processing large quantities of a hostmedium, for example water, that is laden with microorganisms or othersuspended particles. Various implementations of the current subjectmatter can efficiently trap, concentrate, and separate suchmicroorganisms and particles from the host medium. Systems, methods, andthe like according to the current subject matter can rupture the cellwalls and cellular membranes of microorganisms and can also concentrateand remove metal, metal oxide, and other types of particles withoutclogging a filter or a membrane.

Ultrasound waves can also rupture the cellular walls of microorganismssuch as Giardia (6-10 microns), Cryptosporium (4-7 microns) andTrematodes. Acoustophoresis can separate smaller microorganisms such asLepospira, and Salmonella from water sources for human and livestockconsumption. Acoustophoresis can be used to sort particles of differentsizes, density, or compressibility in a single pass through anacoustophoretic cavity.

Some implementations of the current subject matter employ in situelectrochemical generation of ozone in conjunction with standingacoustic waves generated by ultrasonic transducers to achieve separationand concentration of secondary-phase and dissolved components from wateror other host media. Electrochemically generated ozone can induceprecipitation of dissolved metals by formation of metal oxides and alsodestroy small organisms, such as for example viruses, bacteria spores,and the like. Additionally, reactions of ozone with dissolved organiccompounds can reduce or eliminate toxicity of these compounds. In somecases, the resulting products of such reactions can be less soluble orless chemically stable in water. Ozone can also enhance destruction ofsmall organisms in the size range from 10 nm to about 1-2 microns. Whenused in conjunction with the elevated pressures created at nodes of anacoustic standing wave, ozone solubility in the fluid medium (forexample water) can be increased. This increased solubility of ozonecreates an increased concentration of ozone in the fluid phase, whichcan enhance destruction of organic compounds and microorganisms and alsospeed up oxidation of dissolved metals to form less soluble chemicalspecies that are more readily removed from the fluid medium.

Ozone can be produced directly in water, for example by electrochemicalgeneration. The technique can involve lead oxide as a catalytic surface,an acidic or perfluorinated electrolyte, and a platinum counterelectrode. In this technique, as little as 2-3 volts can be required. Aperfluorinated polymeric electrolyte and non-toxic electrodes such asplatinum black, inert noble metals, and glassy carbon electrodes aresome non-toxic approaches to ozone generation in an acoustic resonatorwhere the ozone is used for its ability to precipitate dissolved metals,destroy small organisms and destroy dissolved organics. Precipitatedsubstances can be collected in an acoustic standing wave where theacoustic standing wave also crushes larger organisms (10-1000 microns).

Other advantages of the current subject matter can include, but are notlimited to, use of acoustophoresis for separations in extremely highvolumes and in flowing systems with very high flow rates. Micron-sizeparticles, for which the acoustophoretic force is quite small, cannonetheless be agglomerated into larger particles that are readilyremoved by gravitational settling. For example, Bacillus cereusbacterial spores (a model for anthrax) can be trapped in anacoustophoretic cavity embedded in a flow system that can processdrinking water at rates up to 120 mL/minute (1 cm/second linear flow).Concentration ratios of 1000 or more are possible using a single-passacoustocollector. Other, larger fluid flow rates are possible usinglarger scale flow chambers.

More specifically, the current subject matter describes an apparatusincluding a flow chamber with an inlet and an outlet through which isflowed a mixture of a fluid and a particulate and two or more ultrasonictransducers embedded in or outside of a wall of said flow chamber. Whenthe two or more ultrasonic transducers are located outside the flowchamber wall the thickness of the flow chamber wall can be tuned tomaximize acoustic energy transfer into the fluid. The ultrasonictransducers are arranged at different distances from the inlet of theflow chamber. The ultrasonic transducers can be driven by anoscillating, periodic, or pulsed voltage signal of ultrasonicfrequencies. The apparatus also includes two or more reflectorscorresponding to each ultrasonic transducer located on the opposite wallof the flow chamber from to the corresponding transducer. Eachultrasonic transducer forms a standing acoustic wave at a differentultrasonic frequency. Each frequency can be optimized for a specificrange of particle sizes in the fluid.

The fluid can be flowed horizontally through the flow chamber. The fluidcan be water. The particulate can be selected from microalgae, yeast,fungi, bacteria, spores, gases or oils, metal oxides, metal particles,clays, dirt, plastics, or any particulate with a non-zero contrastfactor. The oscillating, periodic, or pulsed voltage signal ofultrasonic frequencies can be in the range of 10 kHz to 100 MHz.

The apparatus can contain three, four, five, or more ultrasonictransducers. Each transducer forms a standing acoustic wave at adifferent ultrasonic frequency and each frequency can be optimized for aspecific range of particle sizes in the fluid.

The apparatus can be used to produce two or more acoustic standing wavesin the fluid. The standing waves can be perpendicular to the directionof the mean flow in the flow channel. The standing waves can have ahorizontal or vertical orientation. The standing waves can then exertacoustic radiation force on the particulate, such that the particulateis trapped in the acoustic field against the fluid drag force. Thus, theparticulate is concentrated in the acoustic field over time. Thefrequency of excitation of the standing waves can be constant or bevaried in a sweep pattern. The sweep pattern variation can be used totranslate the collected particles along the direction of the acousticstanding waves to either the transducer face or to the reflector face.

The apparatus can also include a collection pocket positioned on thetransducer or on the wall of the flow chamber opposite of thetransducer. The pocket can be planar, conical, curved, or spherical inshape.

The ultrasonic transducer can be made of a piezo-electric material.

The apparatus can also include an additional one or more transducersembedded in the flow channel wall or outside of the vessel wall, withthe wall thickness tuned to maximize acoustic energy transfer. For eachtransducer a reflector is positioned on the opposite wall of the flowchamber. The collection pocket can also have a first door that seals thepocket away from the fluid. The collection pocket can also be connectedto a conduit. This conduit can include a second door which preventsentry of fluid from the flow chamber into the conduit when the firstdoor is open.

The apparatus can also include a device that electrochemically generatesozone. The device can be an electrochemical sandwich system forgenerating ozone underwater comprising a layer of platinum mesh, over alayer of platinum black, over a layer of Nafion®(tetrafluoroethylene-perfluoro-3,6-dioxa-4-methyl-7-octenesulfonic acidcopolymer), over a layer of graphite, over a layer of platinum mesh. Thelayers are held together with nylon screws and nuts. The system can beoperated at between 1 and 100 volts (DC). The system can also be used toinduce the precipitation of dissolved metals and to react the ozone withmetal ions to produce metal oxides in water. Also, the system can beused to kill, through oxidation, suspended virus particles, bacterialspores, and microorganisms in the size range of 1 micron to 100 microns.

The current subject matter also describes a method of separatingparticulate from a fluid comprising flowing the fluid past two or morepositions; and forming acoustic standing waves at the two or morepositions. Each standing acoustic wave can be maintained at a differentultrasonic frequency and each ultrasonic frequency can be optimized fora specific range of particle sizes. The particulate of the optimizedsize is trapped in its corresponding acoustic standing wave against theflow of the fluid. Thus, the particulate is concentrated in itscorresponding acoustic standing wave.

This method can further include sweeping the frequency of the acousticstanding wave thereby directing the concentrated particulate into acollection pocket. The two or more acoustic standing wave can be apulsed waveform resulting in high intensity acoustic pressure. The highintensity acoustic pressure can have sufficient amplitude to rupture thecell wall and cellular membranes of microorganisms.

The method can also include the electrochemical generation of ozone. Theozone can be generated in sufficient quantity to destroy dissolvedmetals, dissolved organics, and submicron organisms and collection ofprecipitated metal oxides and microorganisms in the size range of 1-100microns.

The ozone can be produced by an electrochemical sandwich system forgenerating ozone underwater comprising a layer of platinum mesh, over alayer of platinum black, over a layer of Nafion®, over a layer ofgraphite, over a layer of platinum mesh. The layers can be held togetherwith nylon screws and nuts. The system can be operated at between 1 and100 volts (DC). The system can also be used to induce the precipitationof dissolved metals and react the ozone with metal ions to produce metaloxides in water. The system can also be used to kill, through oxidation,suspended virus particles, bacterial spores, and microorganisms in thesize range of 1 micron to 100 micron.

The details of one or more variations of the subject matter describedherein are set forth in the accompanying drawings and the descriptionbelow. Other features and advantages of the subject matter describedherein will be apparent from the description and drawings, and from theclaims.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, show certain aspects of the subject matterdisclosed herein and, together with the description, help explain someof the principles associated with the disclosed implementations.

FIG. 1 shows a schematic showing an apparatus that includes showing flowchannels, acoustic transducer, reflective surface, and a collectionpocket, for the harvesting of microalgae (similar to othermicroorganisms) and/or dirt particles through acoustophoretic trapping.

FIG. 2 shows a graph showing acoustic force operating on micron-sizeparticles as a function of the particle (or droplet) radius at afrequency of 1 MHz and an acoustic pressure amplitude of 0.5 MPa.

FIG. 3 shows a set of photomicrograph of acoustophoretic trapping of thealgae Dunaliella salina in flowing water.

FIG. 4 shows a series of three photos (at 10× magnification) taken atone second intervals to show gravitational settling of microalgae afterfluid flow has been stopped and the acoustic field has been turned off.

FIG. 5 shows a 10× magnification photograph showing collection ofbacterial spore, B. cerius, [501] from flowing water in an acousticchamber.

FIG. 6 shows a 10× magnification photograph showing collection of ironoxide particles from flowing water [601] in an acoustic chamber.

FIG. 7 shows a schematic diagram of a system of acoustophoresis cellsoperating at different frequencies for removal of particles of differentsizes and densities.

FIG. 8 shows a graph illustrating a frequency sweep used to translatetrapped particles along the direction of an acoustic field.

FIG. 9 shows a perspective diagram of an apparatus for trapping,concentration, collection, etc. of microorganisms and inorganicparticles and their separation from the host medium, containing multiplesystems in line.

FIG. 10 shows a schematic diagram of an electrochemical sandwichstructure used to generate ozone that can be inserted in an acousticresonance chamber.

FIG. 11 shows a schematic diagram of an electrochemical cell inside anacoustic chamber.

When practical, similar reference numbers denote similar structures,features, or elements.

DETAILED DESCRIPTION

An acoustophoretic separator can be created in some implementationsusing a piezoelectric acoustic transducer and an opposing reflectionsurface (or a second transducer) to set up a resonant standing wave inthe fluid of interest. The ultrasonic standing waves create localizedregions of high and low pressure, corresponding to high and low densityof the fluid. Secondary phase contaminants are pushed to the standingwave nodes or antinodes depending on their compressibility and densityrelative to the surrounding fluid. Particles of higher density andcompressibility (e.g., bacterial spores) move to the nodes in thestanding waves while secondary phases of lower density (such as oils)move to the antinodes. The force exerted on the particles also dependson their size, with larger particles experiencing larger forces.

The acoustic radiation force (F_(ac)) acts on the secondary-phaseparticles (or organisms), pushing them to the nodes (or antinodes) ofthe acoustic standing wave. The magnitude of the force depends on theparticle density and compressibility relative to the fluid medium, andincreases with the particle volume.

Besides microorganisms, the acoustic pressures of the standing wave canalso separate low-density droplets and higher density particles, such asmetal oxides (in the size range of 0.2 microns to 100 microns). FIG. 2shows a chart illustrating the acoustic force that operates on fourdifferent secondary phases in water as a function of the particle (ordroplet) radius. The four secondary phases are hexanes (a mixture ofhydrocarbons, a model for oils, represented by line at the top of thegraph), red blood cells (a model for biological cells) and bacterialspores both of which are represented by the lines in the center of thegraph, and paramagnetic polystyrene beads (examples of particles withdensity and size similar to metal oxide particles represented by theline at the bottom of the graph). The forces for an applied acousticfrequency of 1 MHz (typical for an ultrasonic transducer) and anacoustic pressure of 0.5 MPa maximum at the antinodes (readily achievedin water) are shown in FIG. 2. For microorganisms in the range of 3-10microns, the acoustic force can crush/rupture their cell walls. Largerorganisms in the range of 10-100 microns can experience organ failureand thus organism death as a result of the acoustic pressure.Achievement of higher applied acoustic frequencies and higher acousticpressures can afford better separation of smaller metal oxide particlesas well as particles of other compositions, for example those on theorder of 10 nm in diameter.

An ultrasonic transducer operating at a fixed frequency f (Hz) cancreate an acoustic standing wave in a fluid-filled cavity. The standingwave can be characterized by a local pressure p that is a function ofposition (x) and time (t),

p(x,t)=P cos(kx)sin(ωt),  (1)

where P is the amplitude of the acoustic pressure; k is the wave number(equal to 2π/λ, where λ is the wavelength), and ω=2πf, where ω is theangular frequency. The pressure of the acoustic wave produces anacoustic radiation force F_(ac) on secondary-phase elements according to

$\begin{matrix}{{F_{ac} = {X\; \pi \; R_{p}^{3}k\frac{P^{2}}{\rho_{f}c_{f}^{2}}{\sin \left( {2k\; x} \right)}}},} & (2)\end{matrix}$

where R_(p) is the particle radius, ρ_(f) is the density of the fluidmedium, c_(f) is the speed of sound in the fluid, and X is the acousticcontrast factor, defined by

$\begin{matrix}{{X = {\frac{1}{3}\left\lbrack {\frac{{5\Lambda} - 2}{1 + {2\Lambda}} - \frac{1}{\sigma^{2}\Lambda}} \right\rbrack}},} & (3)\end{matrix}$

where Λ is the ratio of the particle density to fluid density and σ isthe ratio of the speed of sound in the particle to the sound speed inthe fluid. The acoustic radiation force acts in the direction of theacoustic field and is proportional to the product of acoustic pressureand acoustic pressure gradient. An inspection of the acoustic radiationforce shows that it is proportional to the particle volume, frequency(or wave number), the acoustic energy density (or the square of theacoustic pressure amplitude), and the acoustic contrast factor. Thespatial dependency has twice the periodicity of the acoustic field. Theacoustic radiation force is thus a function of two mechanicalproperties: density and compressibility. Examples are shown in Table 1.

TABLE 1 Properties of water and 4 selected secondary phases. c (speed ofρ sound in Λ X (density) the medium) (dimension- (dimension- Material(kg/m³) (m/s) less) less) Water 1000 1509 — — Hexanes 720 1303 1.39+0.257 Blood Cells 1125 1900 0.89 −0.30 Bacterial Spores 1100 1900 0.91−0.28 Magnetic beads 2000 1971 0.5 −1.054

For three dimensional acoustic fields, a more general approach forcalculating the acoustic radiation force is needed. Gor'kov'sformulation can be used for this [5]. Gor'kov developed an expressionfor the acoustic radiation force F_(ac) applicable to any sound field.The primary acoustic radiation force is defined as a function of a fieldpotential U, given by

F _(ac)=−∇(U)  (4)

where the field potential U is defined as

$\begin{matrix}{{U = {V_{0}\left\lbrack {{\frac{\langle{p^{2}\left( {x,y,t} \right)}\rangle}{2\rho_{f}c_{f}^{2}}f_{1}} - {\frac{3\rho_{f}{\langle{v^{2}\left( {x,y,t} \right)}\rangle}}{4}f_{2}}} \right\rbrack}},} & (5)\end{matrix}$

and f₁ and f₂ are the monopole and dipole contributions defined by

$\begin{matrix}{{f_{1} = {1 - \frac{1}{{\Lambda\sigma}^{2}}}},{f_{2} = \frac{2\left( {\Lambda - 1} \right)}{{2\Lambda} + 1}},} & (6)\end{matrix}$

where p(x,y,z,t) is the acoustic pressure and v(x,y,z,t) is the fluidparticle velocity. V_(o) is the volume of the particle.

In one implementation that can be used to concentrate and separatemicroorganisms from water, a flow channel can be used to direct flow offluid dispersion, typically water and a secondary-phase component thatis dispersed in the water. The secondary-phase component in one examplecan include microorganisms of interest, such as for example Giardia(6-10 microns), Cryptosporium (4-7 microns) Trematodes (egg and larvalstages are microscopic), Lepospira (6-20 microns), and Salmonella(0.7-1.5 microns). A microorganism of interest can have an averagediameter between 0.5 and 100 microns. A microorganism of interest canalso have an average diameter between 0.5 and 20 microns. Amicroorganism of interest can also have an average diameter between 0.5and 10 microns. An ultrasonic transducer, which in some implementationscan be a piezoelectric transducer, can be located in the wall of theflow channel. The transducer can be driven by an oscillating voltagethat has an oscillation at an ultrasonic frequency that can in someimplementations be in a range of several Megahertz. The voltageamplitude can be between 1 and 100 volts. The transducer, in combinationwith an acoustic reflection surface located at the wall of the flow tubeopposite to the transducer, can generate an acoustic standing waveacross the flow channel. Typical pressure amplitudes in the region ofthe acoustic standing wave or field can be on the order of 0.5 MPa. Suchamplitudes are readily available with piezoelectric transducers. Thispressure can be high enough to crush and destroy organisms above 10microns.

FIG. 3 is a set of photographs showing acoustophoretic collection ofalgae (similar size, density and Young's Modulus as microorganisms suchas Giardia and Cryptosporium) in a flowing water stream. A flat,circular transducer was used in the acoustocollector of FIG. 3. Thepressure field of this transducer is a Bessel function for the radialcomponent in addition to the linear standing wave. The radial componentacts to hold the captured microorganisms in a column [301, 302] againstthe fluid flow. The trapped microorganisms or particles can then befurther concentrated by gravitational settling or by being driven to acollector pocket through a slow frequency sweeping method. Thecollection pocket does not have to be planar, it can also be shaped,conical, curved or spherical. The transducer is at the top, just out ofthe image in FIG. 3. The column of trapped algae [302] is about 2.5 cmhigh×1 cm wide. The ultrasonic pressure nodes can be seen as thehorizontal planes in which the algal cells are captured. The water flowis from left to right. D. salina is the same size/density range as manypathogens.

The pressure amplitudes for this acoustophoresis process can, in someimplementations, advantageously be maintained below the cavitationthreshold values so that a high intensity standing wave field can becreated without generation of cavitation effect or significant acousticstreaming. Acoustic streaming refers to a time-averaged flow of thewater produced by the sound field. Typically, when acoustic streaming isgenerated it results in circulatory motion that can cause stirring inthe water. Cavitation typically occurs when there are gas bodies, suchas air microbubbles, present in the water. The effect of the soundpressure is to create microbubble oscillations which lead tomicrostreaming and radiation forces. Micro-streaming around bubbles leadto shearing flow in the surrounding liquid. This flow containssignificant velocity gradients. If a microorganism is located in thisshearing flow, the uneven distribution of forces on the cell walls canlead to significant shear stresses exerted on the cell walls that maylead to cell wall disruption and rupture. At higher sound intensitylevels, the microbubble oscillations can become more intense, and thebubble can collapse leading to shock wave generation and free radicalproduction. This is termed inertial cavitation. In some alternativeimplementations, a pre-treatment step in which cavitation is induced canbe used to damage or at least partially destroy suspended biologicalcontaminants. Following a region of the flow path where cavitation isinduced, acoustophoresis as described herein can be used to agglomeratesuspended material and also to cause damage to smaller suspendedpathogens that might not be affects by the larger scale forces of acavitation environment.

The acoustophoretic force created by the acoustic standing wave on thesecondary phase component, such as for example the microorganisms orparticles, can be sufficient to overcome the fluid drag force exerted bythe moving fluid on these particles. In other words, the acoustophoreticforce can act as a mechanism that traps the microorganisms in theacoustic field. The acoustophoretic force can drive microorganisms andsuspended particles to the stable locations of minimum acoustophoreticforce amplitudes. These locations of minimum acoustophoretic forceamplitudes can be the nodes of a standing acoustic wave. Over time, thecollection of microorganisms at the nodes grows steadily. Within someperiod of time, which can be minutes or less depending on theconcentration of the secondary phase component, the collection ofmicroorganisms can assume the shape of a beam-like collection ofmicroorganisms with disk-shaped collections of microorganisms. Each diskcan be spaced by a half wavelength of the acoustic field. The beam ofdisk-shaped collections of microorganisms can be “stacked” between thetransducer and the opposing, acoustically-reflective flow-tube wall, asshown as [501] in FIG. 5. In this manner, acoustophoretic forces cantrap and concentrate microorganisms in the region of the acoustic fieldwhile the host medium continues to flow past the concentratedmicroorganisms.

The process of collecting microorganisms can continue until very largevolumes of the host medium have flowed through the trapping region andthe capture of the containing microorganisms has been attained. Furtherseparation of the concentrated microorganisms from the host medium canbe achieved by one or more methods. For a horizontal flow of the hostmedium, gravitational settling can be used to drive the concentratedmicroorganisms into collector pockets, demonstrated in FIG. 4 if themicroorganisms have a greater density than the host fluid [401, 402 and403]. If the microorganisms are less dense than the host fluid, theconcentrated microorganisms will gain buoyancy and float. For verticalor horizontal flow of the host medium, a slow frequency sweeping methodcan be used to translate the microorganisms into collector pockets. Inthis method, the frequency of the acoustic standing wave can be slowlyswept over a small frequency range spanning at least a range of twotimes the frequency corresponding to the lowest-order standing wave modeof the cavity. The sweep period can be, in one example, on the order ofone second. This frequency sweeping method can slowly translate thecollected microorganisms in the direction of the acoustic field towardsone of the walls of the flow chamber where the microorganism can becollected for further processing. This sweep is illustrated in FIG. 8.

In an alternative implementation, the piezoelectric transducer can bedriven by a pulsed voltage signal that includes short-duration, large,positive-amplitude voltage spikes, followed by a longer duration of noapplied voltage signal. This pulsed pattern can be repeated according toa repetition rate or period. This excitation can generate very largeamplitude compressive pressure pulses in water that can be sufficient torupture the cell walls and cellular membranes of microorganisms prior toacoustophoresis collection.

In another implementation, a piezoelectric transducer can be driven by apulsed voltage signal that includes short-duration, large,negative-amplitude voltage spikes, followed by a longer duration of noapplied voltage signal. This pulsed pattern can be repeated according toa repetition rate or period. This excitation can generate very largeamplitude expansion-type pressure pulses in water that can be sufficientto rupture the cell walls and cellular membranes of microorganisms priorto acoustophoresis collection.

The current subject matter can provide large-scale acoustophoretictechnology to collect and process microorganism contaminated water toreduce or eliminate pathogens in the water. In an implementation, thiseffect can be accomplished using a simple one-step process involvingacoustophoresis which simultaneously ruptures large (>10 micron)organisms and collects smaller organisms (<10 microns) and suspendedparticles to acoustic pressure nodes where they accumulate andagglomerate such that gravitational or other processes can effectivelyremove finally dropping into a collection port for removal. The processcan be applied in either batch or continuous flow reactorconfigurations. The current subject matter can also be used to collect,remove, etc. metal oxides and metal particles form water to purifywater, for example drinking water. Both the inorganic particles and themicroorganisms can be simultaneously collected in a filter free process.

In one implementation, a system such as that shown in FIG. 1 forconcentrating and separating microorganisms from a host medium such aswater can include a flow chamber with an inlet [101] and outlet [104].The flow direction can in some variations be oriented in a horizontaldirection. The flow chamber can receive a mixture of water including asuspended phase that can include microorganisms, such as microalgae,yeast, fungi, bacteria, or spores as well as other, non-biologicalparticles (e.g. metal oxides, clay, dirt, etc.). The flow chamber canhave macro-scale dimensions. In other words, the dimensions of thecross-section of the flow chamber are much larger than the wavelengthcorresponding to the generated sound. The system also includes anultrasonic transducer [3], that can be embedded in a wall of the flowchamber or located outside of the flow chamber. The ultrasonictransducer can include a piezo-electric material and can be driven by anoscillating voltage signal of ultrasonic frequencies. Ultrasonictransducers other than piezoelectric transducers can be used.

The ultrasonic frequencies can be in the range from 1 kHz to 100 MHz,with amplitudes of 1-100 of volts, normally acting in the tens of volts.The ultrasonic frequencies can be between 200 kHz and 3 MHz. Theultrasonic frequencies can be between 1 and 3 MHz. The ultrasonicfrequencies can be 200, 400, 800, 1000 or 1200 kHz. The ultrasonicfrequencies can be between 1 and 5 MHz. A reflector [105] can be locatedopposite to the transducer, such that an acoustic standing wave isgenerated in the host medium. The acoustic standing wave can be orientedperpendicularly to the direction of the mean flow in the flow channel.In some implementations, the acoustic standing wave can be orientedvertically for a horizontal fluid flow direction. The acoustic fieldexerts an acoustic radiation force, which can be referred to as anacoustophoretic force, on the suspended phase component. The suspendedphase can be trapped in the acoustic field against the fluid drag force,thereby resulting in large scale collection of the suspended phasecomponent. Switching off the water flow through the flow chamber canresult in gravitational settling of the collected particles to thebottom of the flow chamber.

In optional variations, the system can be driven at a constant frequencyof excitation and/or with a frequency sweep pattern or step pattern, asshown in FIG. 8. The effect of the frequency sweeping or stepping can beto translate the collected particles along the direction of the acousticstanding wave to either the transducer face or to the opposite reflectorface. A collection pocket or other void volume can be positionedopposite to the transducer such that settled particles are collected inthe collection pocket, for example as shown in the set of images in FIG.4. The collection pocket can include one or more butterfly valves orother mechanisms for removing a slurry containing water with a highsuspended phase concentration from the flow chamber. In this manner,after the suspended phase settles into the collection pocket, thesettled suspended materials are removed from the flowing water stream.

The flow direction of a system can be oriented in a direction other thanhorizontal. For example, the fluid flow can be vertical either upward ordownward or at some angle relative to vertical or horizontal. Theposition of the acoustic transducer can be chosen so that the acousticfield is in a direction such that the translation of particles into acollection pocket can be achieved by a frequency sweeping or steppingmethod. More than one transducer can be included in the system. Forexample, as shown in FIG. 9, each transducer can have its own reflectorand can include a collector pocket that can further include a mechanismfor removing concentrated slurry of suspended phase material form thewater flow. A set systems, as shown in FIG. 9, can have each system'stransducer set at different frequencies can be used to efficientlyconcentrate and/or remove suspended material such as metal oxideparticles and similar density particles having a range of sizes anddensities from a flowing liquid medium.

Acoustic systems such as that shown in FIG. 1 can also be seriallyconnected with different resonant transducers for greaterparticle/organism capture efficiency. A schematic diagram of such animplementation is shown in FIG. 7 and FIG. 9. The system can include aseries of individual units similar to those shown in FIG. 1. The systemshown in FIG. 1 has been optimized to capture of metal oxide particles(as well as particles of other compositions) in the size range of 0.2 to100 microns and to capture/destroy microorganisms in the size range of 1to 150 microns. Individual transducers or arrays of transducers aretuned to allow different acoustic frequencies to capture differentranges of particle/organism sizes.

The system of FIG. 7 includes cells operating at 200 kHz [701], 400 kHz[702], 600 kHz [703], 800 kHz [704], 1000 kHz [705] and 1200 kHz [706].Each cell has been optimized for a specific range of particle/organismsize. The overall system as shown in FIG. 1 is capable of processing 1gal/min of water. Parallel or serial arrays similar to that shown can beconstructed to process a variety of volumetric flow rates.

FIG. 9 shows a schematic with three transducers [903, 904, 905] on thewall of a flow chamber with an inlet [902] and an outlet [901]. Eachtransducer has a corresponding reflector [906, 907 908] on the oppositewall of the flow chamber.

Various implementations of the current subject matter relate to the useof electrochemical generation of ozone under water in conjunction withan acoustophoretic process to precipitate and remove dissolved metalsand destroy organisms and dissolved organics and suspended orparticulate phase materials. Acoustophoresis can be induced by astanding acoustic wave created ultrasonically. Production of ozone insitu can induce precipitation of dissolved contaminants, for examplemetal oxides, as well as partial or complete destruction of dissolvedorganic compounds.

An electrochemical sandwich system that includes a layer of platinummesh (contact), platinum black (anode), Nafion® (electrolyte), graphite(cathode), and platinum mesh (contact) held together with nylon screwsand nuts can be used in the acoustophoretic cell to generate ozoneunderwater. Other possible electrodes can include, but are not limitedto, stainless steel, noble metals, Ta, Hf, Nb, Au, Ir, Ni, Pt/W alloy,lead oxide, or oxides of titanium. FIG. 10 shows a schematic diagram ofan ozone generator that can be used in conjunction with implementationsof the current subject matter. A five layer “sandwich” type constructioncan be used that includes platinum mesh [1001], platinum black, anode,[1002] 3) Nafion®(tetrafluoroethylene-perfluoro-3,6-dioxa-4-methyl-7-octenesulfonic acidcopolymer) [1003], 4) carbon black, cathode, [1004] and 5) platinum mesh[1005]. The layers are held together with nylons screws [1006]. A devicesuch as this [1102] can be positioned in the bottom of an acousticresonator [1101] as shown in the schematic diagram of FIG. 11.

In some implementations, ozone can be produced by electrochemical meansin an acoustic resonance chamber where water is flowing. The ozone candestroy, through oxidation, dissolved metals, dissolved organics,submicron organisms, and the like. The acoustic field can concentrateand separate microorganisms and other suspended particulate matter fromwater.

Aspects of the current subject matter described may be realized indigital electronic circuitry, integrated circuitry, specially designedASICs (application specific integrated circuits), computer hardware,firmware, software, and/or combinations thereof. These variousimplementations may include implementation in one or more computerprograms that are executable and/or interpretable on a programmablesystem including at least one programmable processor, which may bespecial or general purpose, coupled to receive data and instructionsfrom, and to transmit data and instructions to, a storage system, atleast one input device, and at least one output device.

These computer programs (also known as programs, software, softwareapplications or code) include machine instructions for a programmableprocessor, and may be implemented in a high-level procedural and/orobject-oriented programming language, and/or in assembly/machinelanguage. As used herein, the term “machine-readable medium” refers toany computer program product, apparatus and/or device (e.g., magneticdiscs, optical disks, memory, Programmable Logic Devices (PLDs)) used toprovide machine instructions and/or data to a programmable processor,including a machine-readable medium that receives machine instructionsas a machine-readable signal. The term “machine-readable signal” refersto any signal used to provide machine instructions and/or data to aprogrammable processor.

The subject matter described herein may be implemented in a computingsystem that includes a back-end component (e.g., as a data server), orthat includes a middleware component (e.g., an application server), orthat includes a front-end component (e.g., a client computer having agraphical user interface or a Web browser through which a user mayinteract with an implementation of the subject matter described herein),or any combination of such back-end, middleware, or front-endcomponents. The components of the system may be interconnected by anyform or medium of digital data communication (e.g., a communicationnetwork). Examples of communication networks include a local areanetwork (“LAN”), a wide area network (“WAN”), and the Internet.

The computing system may include clients and servers. A client andserver are generally remote from each other and typically interactthrough a communication network. The relationship of client and serverarises by virtue of computer programs running on the respectivecomputers and having a client-server relationship to each other.

EXAMPLES Example 1 Separation of Algae from Water Using an AcousticStanding Wave

In an illustrative implementation, microorganisms including microalgaeand bacterial spores were removed from a flowing water stream. As ademonstration of the current subject matter, algae of the halophilicDunaliella Salina (similar in size and density to many pathogenicorganisms) were grown in a bottle filled with salt water and placedunder a grow light. The algae are removed from the bottle through tubesthat pass them into a flow channel and past an acoustic transducer. Theapparatus is shown in FIG. 1. The flow chamber was horizontal with thetransducer on top facing downward. This resulted in a verticallyoriented acoustic standing wave. The transducer used in the system ofFIG. 1 is a PZT-4 2 MHZ transducer. Other transducers can be used.

The acoustic transducer was connected to an amplifier which receives itssignal from a function generator and operates at about 15 V_(rms) in thecurrent example. Once the fluid flow and the acoustic transducer wereturned on, trapping and concentration of microalgae and other particlesstarted quickly. The microalgae and/or particles were trapped in theacoustic field against the fluid drag force by means of the action ofthe acoustic radiation force. The collection of microalgae and/orparticles continued over time and eventually, typically after severalminutes, large, beam-like collections of microalgae and/or particles canbe seen in the region between the transducer face and the oppositionreflective wall. A typical result of the acoustic trapping of microalgaeand/or particles for about 3 to 5 minutes in the apparatus of FIG. 1, isshown in the photomicrograph of FIG. 3.

Example 2 Breaking Cell Wall and Cell Membranes of Microorganisms Usingan Acoustic Standing Wave

Ultrasonic cavitation can be used to crush larger organisms (>10microns). Some implementations of the current subject matter use highintensity ultrasound below an amplitude that causes cavitation. Breakageof cell walls and cellular membranes of microorganisms occurs due to thehigh pressures caused at the nodes of the acoustic standing wave. As anexample of the potential of this approach, a suspension of concentratedmicroalgae of mixed sizes (mixed ages, 0.1 mm to 1.0 mm) of the nematodeCaenorhabditis elegans were placed in a vertical glass tube with a PZT-42.3 MHz transducer mounted on the bottom with a glass plate on the topas the acoustic reflector. By simply subjecting the organisms toacoustophoresis without cavitation the smaller worms were crushed openand the larger organisms suffered catastrophic neuromuscular problems.This occurred when the pressure amplitude was about 0.5 MPa at theacoustic nodes.

In further implementations, a cavitation technique can be incorporatedas a pre-treatment step. A system such as that shown in FIG. 1 can beoperated in cavitation mode to enhance the killing of microorganisms inthe size scale from 1 micron to 100 microns. During the cavitationprocess, the cell wall and cellular membranes can be broken and theproteins released from the cells. In one illustrative example, anacoustic field resulting in cavitation was applied for about fiveminutes. Within a few minutes most of the organism debris—the cell walland cellular debris falls to the bottom of the acoustic chamber.

Example 3 Separating Iron Oxide Particles from Water Using an AcousticStanding Wave

The current subject matter can also concentrate and/or removemicron-scale metal oxide particles. As a demonstration of thiscapability, 10 micron iron oxide particles were suspended in water andpassed through the apparatus shown in FIG. 3. In this demonstration, theflow chamber is horizontal with the transducer on top facing downward.The acoustic standing wave is in the vertical direction. The transduceris a PZT-4 2 MHZ transducer. A peristaltic pump is used to generatefluid flow rates that are most typically about 50 ml/min.

The acoustic transducer is connected to an amplifier which receives itssignal from a function generator and operates at about 15 V_(rms). Oncethe fluid flow and the acoustic transducer are turned on, trapping andconcentration of iron oxide begins instantaneously or nearlyinstantaneously. The oxide particles are trapped in the acoustic fieldagainst the fluid drag force by means of the action of the acousticradiation force. The photomicrograph of FIG. 6 illustrates the resultsof such a test.

The implementations set forth in the foregoing description do notrepresent all implementations consistent with the subject matterdescribed herein. Instead, they are merely some examples consistent withaspects related to the described subject matter. Although a fewvariations have been described in detail above, other modifications oradditions are possible. In particular, further features and/orvariations can be provided in addition to those set forth herein. Forexample, the implementations described above can be directed to variouscombinations and subcombinations of the disclosed features and/orcombinations and subcombinations of several further features disclosedabove. In addition, the logic flows depicted in the accompanying figuresand/or described herein do not necessarily require the particular ordershown, or sequential order, to achieve desirable results. Otherimplementations may be within the scope of the following claim.

1. An apparatus comprising: a flow chamber with an inlet and an outletthrough which is flowed a mixture of a fluid and a particulate; two ormore ultrasonic transducers embedded in a wall of said flow chamber orlocated outside the flow chamber wall; and two or more reflectorscorresponding to each transducer located on the opposite wall of theflow chamber from each corresponding transducer; wherein if the two ormore ultrasonic transducers are located outside the flow chamber wallthe thickness of the flow chamber wall is tuned to maximize acousticenergy transfer into the fluid, wherein the transducers are arranged atdifferent distances from the inlet, wherein the ultrasonic transducersare driven by an oscillating, periodic, or pulsed voltage signal ofultrasonic frequencies, wherein each transducer forms a standingacoustic wave at a different ultrasonic frequency and wherein eachultrasonic frequency is optimized for a specific range of particlesizes.
 2. The apparatus of claim 1, wherein the fluid is flowedhorizontally through the flow chamber.
 3. The apparatus of claim 1,wherein the fluid is water.
 4. The apparatus of claim 1, wherein theparticulate is selected from the group consisting of microalgae, yeast,fungi, bacteria, spores, gases or oils, metal oxides, metal particles,clays, dirt, plastics, and any particulate with a non-zero contrastfactor.
 5. The apparatus of claim 1, wherein the oscillating, periodic,or pulsed voltage signal of ultrasonic frequencies is in the range of 10kHz to 100 MHz.
 6. The apparatus of claim 1, comprising three or moreultrasonic transducers embedded in a wall of said flow chamber orlocated outside the flow chamber wall, wherein when the three or moreultrasonic transducers are located outside the flow chamber wall thethickness of the flow chamber wall is tuned to maximize acoustic energytransfer into the fluid, wherein the transducers are arranged atdifference distances from the inlet and wherein the ultrasonictransducers are driven by an oscillating, periodic, or pulsed voltagesignal of ultrasonic frequencies and three or more reflectorscorresponding to each transducer located on the opposite wall of theflow chamber from each corresponding transducer.
 7. The apparatus ofclaim 1, comprising four or more ultrasonic transducers embedded in awall of said flow chamber or located outside the flow chamber wall,wherein when the four or more ultrasonic transducers are located outsidethe flow chamber wall the thickness of the flow chamber wall is tuned tomaximize acoustic energy transfer into the fluid, wherein thetransducers are arranged at difference distances from the inlet andwherein the ultrasonic transducers are driven by an oscillating,periodic, or pulsed voltage signal of ultrasonic frequencies and four ormore reflectors corresponding to each transducer located on the oppositewall of the flow chamber from each corresponding transducer.
 8. Theapparatus of claim 1, comprising five or more ultrasonic transducersembedded in a wall of said flow chamber or located outside the flowchamber wall, wherein when the five or more ultrasonic transducers arelocated outside the flow chamber wall the thickness of the flow chamberwall is tuned to maximize acoustic energy transfer into the fluid,wherein the transducers are arranged at difference distances from theinlet and wherein the ultrasonic transducers are driven by anoscillating, periodic, or pulsed voltage signal of ultrasonicfrequencies and five or more reflectors corresponding to each transducerlocated on the opposite wall of the flow chamber from each correspondingtransducer.
 9. The apparatus of claim 1, wherein each transducer isoptimized for a specific range of particles selected from the groupconsisting of microalgae, yeast, fungi, bacteria, spores, gases or oils,metal oxides, metal particles, clays, dirt, plastics, and anyparticulate with a non-zero contrast factor.
 10. The apparatus of claim1, wherein the two or more acoustic standing waves are perpendicular, tothe direction of the mean flow in the flow channel.
 11. The apparatus ofclaim 10, wherein the two or more acoustic standing wave has ahorizontal orientation.
 12. The apparatus of claim 10, wherein the twoor more acoustic standing wave has a vertical orientation.
 13. Theapparatus of claim 10, wherein the two or more acoustic standing wavesexert acoustic radiation force on the particulate for which theultrasonic frequency is optimized for, such that the particulate istrapped in its corresponding acoustic standing wave against a fluid dragforce, and wherein the particulate is concentrated in the acoustic fieldover time.
 14. The apparatus of claim 1 wherein the frequency ofexcitation of the two or more acoustic standing waves is constant. 15.The apparatus of claim 10, wherein the frequency of the two or moreacoustic standing waves vary in a sweep or step pattern.
 16. Theapparatus of claim 10, wherein the collected particles are translatedalong the direction of the acoustic standing wave to either thetransducer face or to the reflector face.
 17. The apparatus of claim 1,further comprising a collection pocket positioned on the transducer. 18.The apparatus of claim 17, wherein the collection pocket is planar,conical, curved, or spherical in shape.
 19. The apparatus of claim 17,wherein the collection pocket further comprises a first door, whereinthe door seals the pocket away from the fluid.
 20. The apparatus ofclaim 19, wherein the collection pocket connects to a conduit, whereinthe connection further comprises a second door which prevents entry offluid from the flow chamber into the conduit when the first door isopen.
 21. The system of claim 1, further comprising a collection pocketpositioned on the wall of the flow chamber opposite of the transducer.22. The apparatus of claim 21, wherein the collection pocket is planar,conical, curved, or spherical in shape.
 23. The apparatus of claim 21,wherein the collection pocket further comprises a first door, whereinthe door seals the pocket away from the fluid.
 24. The apparatus ofclaim 23, wherein the collection pocket connects to a conduit, whereinthe connection further comprises a second door which prevents entry offluid from the flow chamber into the conduit when the first door isopen.
 25. The apparatus of claim 1, wherein the two or more ultrasonictransducers are made of a piezo-electric material.
 26. The apparatus ofclaim 1, further comprising a device that electrochemically generatesozone.
 27. A method of separating particulate from a fluid comprising:flowing the fluid past two or more positions; and forming acousticstanding waves at the two or more positions, wherein each standingacoustic wave is maintained at a different ultrasonic frequency, whereineach ultrasonic frequency is optimized for a specific range of particlesizes and wherein particulate of the optimized size is trapped in itscorresponding acoustic standing wave against the flow of the fluid,thereby concentrating the particulate in its corresponding acousticstanding wave.
 28. The method of claim 27, further comprising sweepingthe frequency of the acoustic standing wave thereby directing theconcentrated particulate into a collection pocket.
 29. The method ofclaim 27, wherein the two or more acoustic standing waves are pulsedwaveforms resulting in high intensity acoustic pressure.
 30. The methodof claim 29, wherein the high intensity acoustic pressure can havesufficient amplitude to rupture the cell wall and cellular membranes ofmicroorganisms.
 31. The method of claim 27, further comprisingelectrochemically generating ozone, wherein the ozone is generated insufficient quantity to destroy dissolved metals, dissolved organics, andsubmicron organisms.
 32. The method of claim 27, further comprisingelectrochemically generating ozone, wherein the ozone is generated insufficient quantity to collect precipitated metal oxides andmicroorganisms in the size range of 1-100 microns.
 33. The method ofclaim 32, wherein the ozone is produced by an electrochemical sandwichsystem comprising a layer of platinum mesh, over a layer of platinumblack, over a layer oftetrafluoroethylene-perfluoro-3,6-dioxa-4-methyl-7-octenesulfonic acidcopolymer, over a layer of graphite, over a layer of platinum meshwherein the layers are held together with nylon screws and nuts.
 34. Themethod of claim 33, wherein system is operated at between 1 and 100volts (DC).
 35. An apparatus comprising a layer of platinum mesh, over alayer of platinum black, over a layer oftetrafluoroethylene-perfluoro-3,6-dioxa-4-methyl-7-octenesulfonic acidcopolymer, over a layer of graphite, over a layer of platinum meshwherein the layers are held together with nylon screws and nuts.
 36. Amethod of precipitating dissolved metals in a solution comprisingcontacting the solution comprising dissolved metals to the apparatus ofclaim
 35. 37. A method of killing microorganisms in a solution selectedfrom the group consisting of suspended virus particles, bacterialspores, and microorganisms in the size range of 1 micron to 100 microncomprising contacting the solution comprising dissolved metals to theapparatus of claim
 35. 38. An apparatus for separating particulate froma fluid comprising: a means for flowing the fluid past two or morepositions; and a means for forming acoustic standing waves at the two ormore positions, wherein each standing acoustic wave is maintained at adifferent ultrasonic frequency, wherein each ultrasonic frequency isoptimized for a specific range of particle sizes and wherein particulateof the optimized size is trapped in its corresponding acoustic standingwave against the flow of the fluid, thereby concentrating theparticulate in its corresponding acoustic standing wave.